Method and apparatus for determining the surface level of molten material in a mold

ABSTRACT

The rising level of molten metal in a mold, pertaining, for example, to a continuous casting apparatus, is supervised by electrical resistance wire probes dipping into the mold and short circuited by the molten metal therein. The resistance change in the circuit is ascertained and used as level indication.

United States Patent Schiefer et a];

[451 June 6, 1972 [54] METHOD AND APPARATUS FOR DETERMINING THE SURFACELEVEL OF MOLTEN MATERIAL IN A MOLD [72] Inventors: Peter Schiefer,Muehlheim(Ruhr): Bernd Findeisen, Duisburg-Buchholz, both of Germany[73] Assignee: Mannesmann Aktiengasellschaft, Dusseldorf, Germany [22]Filed: July 24, 1970 [21] Appl.No.: 58,044

[30] Foreign Application Priority Data July 28, 1969 Germany ..P 19 38840.0

[52] US. Cl. ..73/304 R, 164/4 [51] ..B22d 11/10, G01f23/24 [58] Fieldof Search ..73/304 R; 164/4, 150

[56] References Cited UNITED STATES PATENTS 3,369,401 2/1968 Briggs et..73/304 R 3,478,808 11/1969 Adamsm. 164/4 1,532,871 4/1925 Bloch..73/304 R x 3,184,970 5/1965 McNelly ..73/304 R FOREIGN PATENTS ORAPPLICATIONS 1,105,568 4/1961 Germany ..73 304 R Primary Examiner-S.Clement Swisher Assistant Examiner-Frederick Shoon Attorney-Smyth,Roston & Pavitt and Ralf H. Siegemund ABSTRACT The rising level ofmolten metal in a mold, pertaining, for example, to a continuous castingapparatus, is supervised by electrical resistance wire probes dippinginto the mold and short circuited by the molten metal therein. Theresistance change in the circuit is ascertained and used as levelindicat1on.

4 Claims, 1 Drawing Figure METHOD AND APPARATUS FOR DETERMINING THESURFACE LEVEL OF MOLTEN MATERIAL IN A MOLD The present invention relatesto method and equipment for determining the height of the rising surfacelevel of molten material in a mold that is closed at the bottom and isbeing charged. The invention will find particular utility in machinesfor continuous casting of steel particularly during the initial phase ofoperation, when the bottom of the mold is still closed. The problem,thus stated, has not been solved satisfactorily in the past. Inaccordance with the invention, it is suggested to provide two resistancewire probes which extend into the mold, down to the vicinity of thebottom thereof. As molten, liquidous metal, or the like, pours into themold, the probes are interconnected electrically, and the resistance ofthe closed circuit, thus established, decreases with increasing levelheight of the molten metal in the mold. The two probes are connected toa biasing voltage, and the change in resistance in that circuit will bemeasured through measurement of appropriate operating parameters, e.g.,current and/or voltage, for example, by means of suitable resistancemeasuring network. The probes must be chosen to experience a significantchange in resistance within that biasing circuit when the level of metalrises in the mold and shortens the effective portions of the probes inthe circuit.

A particular form of practicing the invention includes metallic wireprobes which melt where submerged in the liquidous metal. The probes maywell consist of the same material that is used for casting. Theresistance of the probes as effective in the circuit varies linearlywith length that is still above the surface level of the molten metaland is, thus, directly representative of the level height in the mold.

The invention will find utility in all methods of casting where thelevel of the molten material may rise for any reason and wherein thatrise, or even the rate of rising, is to be supervised to obtain and tocontrol, for example, a definite rate and speed of filling the mold.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects and featuresof the invention and further objects, features and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawings in which:

The FIGURE illustrates somewhat schematically a continuous castingmachine improved by a supervising circuit in accordance with the presentinvention.

Proceeding now to the detailed description of the drawings, there isillustrated a mold l for continuous casting. The bottom of the mold isshown as having been closed by an ingot blank or stool 2. Liquid metal,such as steel, is poured into the mold be means of a ladle or the like(not shown). The bottom of the mold must remain closed in the mannerillustrated until the molten metal has reached a particular level 3 thatis determined by casting technique generally. Subsequently, the ingotblank is drawn out of the mold and lowered, followed by the castingstring that is formed pursuant to this procedure. Rolls 4 guide thewithdrawal of the ingot blank as well as of the casting string thatfollows.

Having described the background and environment for practicing theinvention, we now turn to particulars thereof, provided for ascertainingthe rising surface level of the molten material in the mold during theinitial phase. The surface level will indeed rise as long as the bottomof the mold is closed by ingot blank 2. There are provided two parallelydisposed probes 5. The probes 5 are constructed from resistance wires ofabout 3 mm diameter. The two probes pertain to an electrical circuitwhich includes a dc. voltage source 6 to obtain operational bias. Thetwo probes 5 connect to terminals of op posite polarity of the voltagesource, so that a current is driven through the circuit to flow throughthe probes and across the molten metal.

initially, probes 5 extend almost all the way to the bottom of the mold.As long as the mold is empty, the circuit is open. As molten metal poursinto the mold, the respective portions of the wires, dipping into theliquidous metal, melt. Nevertheless, the two probes 5 are, and remain,electrically interconnected at or near the surface of the liquid metal.As the mold fills, the length of the probes above the surface level ofthe molten material, declines. The fact that the probes have melted awaybelow that rising level does not change the fact that the two probesremain electrically interconnected by the rather low resistance of themolten material into which they clip.

The resistance of the electric circuit has essentially two components: Rand R,,. Resistance R, is primarily determined by the lengths of theprobes 5 above the surface level in the mold, not yet melted. The othercomponent is essentially the line resistance R,,. As the probes areparallel to each other equidistant spacing is established between themresulting in a constant length current path through the molten metal.Thus, the conditions for electric circuit between the two probes acrossthe molten metal remains essentially independent from the level thematerial in the mold has reached. The resistivity of that path throughthe molten material can be regarded as being included in line resistanceR,., constituting a known and essentially constant parameter.

As the liquid level rises, the resistance R I in the circuit varies(declines) linearly therewith, and the variation can be used asindication for the relative liquid level height in the mold. The circuitbetween the probes is essentially closed always in or directlyunderneath the surface level. probes are connected in series in thecircuit, the level change is effective twice, once in each probe.

For measuring the resistance R in representation of liquid level height,resistance networks known per se are used. The resistance network willbe conventional, and may include source 6 as constant current source(current I). The permissible voltage change may be limited, but mustinclude the range of interest and as needed for measurement. A recordingvoltmeter 7 is connected across the source 6, to register the volt agedrop variations as they result from a change in resistance R,. In orderto compensate the circuit resistance R,., a voltage source 9, providinga compensating voltage U, is connected via a potentiometer 8 inopposition to the measuring voltage as applied to and effective acrossvoltmeter 7. The potentiometer 8 is adjusted for determining theoperating point of measurement, and can be used for calibrating theinstrument 7.

The circuit is shown as a representative example only, a differentcircuit can be employed, using, for example, a constant voltage sourcewhile the voltage drop across a series, constant resistor is used tomeasure the change in probe resistance.

The example above refers specifically to the determination of the levelof the molten metal in the mold of a continuous casting machine,operable particularly upon'starting thereof. The inventive method,however, is applicable equally well for casting of block ingots.

The invention is not limited to the embodiments described above but allchanges and modifications thereof not constituting departures fromthespirit and scope of the invention are intended to be included.

We claim:

1. Apparatus for measuring the rising surface level of molten metal in amold, comprising:

a pair of resistance wire probes made of the same metal as the moltenmetal in the mold and disposed in parallel relationship and dipping intothe mold to extend down to the vicinity of the bottom thereof;

a source of electrical voltage potential connected to the wires of thepair to apply biasing voltage thereto, to provide current flow throughthe wire probes, there being a closed circuit established when the wireprobes are interconnected by molten metal in the mold, the wire probesof the pair being connected in series in the circuit; and

means connected for measuring the change in resistance in the circuit toobtain representation of rising level of molten metal in the mold.

2. Apparatus as in claim 1, the wire probes stationarily disposed to dipinto the mold, the circuit including a resistance measuring circuit.

3. Apparatus for measuring the rising surface level of molten metal in amold, comprising;

a pair of resistance wire probes, made of metal that melts in the moltenmetal in the mold and disposed in parallel 1 relationship and dippinginto the mold to extend down to the vicinity of the bottom thereof;

a source of electrical voltage potential connected to the wires of thepair to apply biasing voltage thereto, to provide current flow throughthewirc probes, there being a closed circuit established when the wireprobes are interconnected by molten metal in the mold, the wire probesof the pair being connected in series in the circuit; and 5 meansconnected for measuring the change in resistance in the circuit toobtain representation of rising level of molten metal in the mold. 4.Apparatus as in claim 3, the wire probes stationarily disposed to dipinto the mold, the circuit including a resistance measuring circuit.

I l l l 1

1. Apparatus for measuring the rising surface level of molten metal in amold, comprising: a pair of resistance wire probes made of the samemetal as the molten metal in the mold and disposed in parallelrelationship and dipping into the mold to extend down to the vicinity ofthe bottom thereof; a source of electrical voltage potential connectedto the wires of the pair to apply biasing voltage thereto, to providecurrent flow through the wire probes, there being a closed circuitestablished when the wire probes are interconnected by molten metal inthe mold, the wire probes of the pair being connected in series in thecircuit; and means connected for measuring the change in resistance inthe circuit to obtain representation of rising level of molten metal inthe mold.
 2. Apparatus as in claim 1, the wire probes stationarilydisposed to dip into the mold, the circuit including a resistancemeasuring circuit.
 3. Apparatus for measuring the rising surface levelof molten metal in a mold, comprising; a pair of resistance wire probes,made of metal that melts in the molten metal in the mold and disposed inparallel relationship and dipping into the mold to extend down to thevicinity of the bottom thereof; a source of electrical voltage potentialconnected to the wires of the pair to apply biasing voltage thereto, toprovide current flow through the wire probes, there being a closedcircuit established when the wire probes are interconnected by moltenmetal in the mold, the wire probes of the pair being connected in seriesin the circuit; and means connected for measuring the change inresistance in the circuit to obtain representation of rising level ofmolten metal in the mold.
 4. Apparatus as in claim 3, the wire probesstationarily disposed to dip into the mold, the circuit including aresistance measuring circuit.